1. Field of the Invention
The present invention relates to a sheet coating apparatus for applying a predetermined coating liquid onto a sheet.
2. Description of the Related Art
In a liquid electrophotographic printer, e.g., a laser printer, in order to prevent a printed image from blotting on paper and to improve the resolution of an image, a coating apparatus for applying a coating liquid such as wax after a printing operation has been proposed. A conventional coating apparatus, as shown in FIG. 1, is configured such that a coating roller 10 and a backup roller 20 are rotatably installed along the traveling path through which a sheet 1 passes, and the coating roller 10 is partially immersed in a storage tank 30 containing a liquid wax W. Accordingly, the wax W sticking to the coating roller 10 is coated onto the printed surface of the sheet 1 passing between the coating roller 10 and the backup roller 20.
However, in the above-described coating system, since there is no means of regulating the amount of wax W moving upward along the surface of the coating roller 10 according to rotation thereof and which is to be coated onto the sheet 1 by the coating roller 10, it is not possible to regulate the amount of coated wax. Thus, the amount of coated wax is nonuniform and excess wax is likely to be coated, which results in increased consumption of a coating liquid. If the content of the coating liquid is reduced, that is, if the content of a liquid carrier which is a solvent contained in the coating liquid, is increased, the amount of the coating liquid consumed can be reduced. However, since the liquid carrier heavily contained in the coating liquid is considerably absorbed into the sheet 1, the image printed on the sheet 1 is likely to blot. In order to overcome the problem of carrier absorption, if the content of the wax is increased, the consumption of the coating liquid increases. Also, since the viscosity of the coating liquid is increased, the flow of the coating liquid is not smooth, and thus the coating thickness becomes nonuniform. Therefore, a coating apparatus which can allow uniform coating while reducing the consumption of a coating liquid, is required.
To solve the above problems, it is an object of the present invention to provide an improved sheet coating apparatus which can uniformly regulate the amount of a coating liquid coated onto a sheet.
Accordingly, to achieve the above object, there is provided a sheet coating apparatus including a storage tank in which a coating liquid having charged coating particles dispersed therein is contained, a development roller rotatably installed to be immersed in the coating liquid, a voltage source for applying a voltage to the development roller, a coating roller rotatably installed in a state in which it is partially immersed in the coating liquid while maintaining a predetermined development gap relative to the development roller, and a compression roller for pressing a sheet passing between the compression roller and the coating roller toward the coating roller while securely rotating with respect to the coating roller, wherein the coating particles adhere to the surface of the coating roller at the development gap due to an electric force to then be coated on the sheet passing between the coating roller and the compression roller.